The first person to bear witness to the existence of the Underpants Gnomes was Tweek Tweak, who always managed to remain awake for their visits due to his heavy coffee addiction. Whenever he attempted to tell others of their existence, people assumed he was hallucinating and overly stimulated. However, when the boys were forced to do a school project with Tweek, they soon realize that the Gnomes are indeed real, and indeed stealing underpants. The reason for the thefts is apparently due to some sort of higher corporate plan. The plan was outlined thus:

Phase 1: Steal Underpants.

Phase 2: ?

Phase 3: Profit

Despite the Gnome's plan being somewhat lacking in certain areas, they are apparently very intelligent in regards to economics and business, teaching the boys about big corporations.

The Underpants Gnomes appear again in "Red Sleigh Down", in which it is revealed that Santa Claus does not hire elves, but rather the Underpants Gnomes to be his holiday helpers. Although they spend most of the year collecting underpants, every Christmas they travel to the North Pole, where they work as central control for Santa's holiday mission. One year, Santa was shot down over Iraq, and the Underpants Gnomes helped the boys locate Jesus Christ to help in an exfiltration mission.

Appearance

Gnomes on the SP site.

Underpants Gnomes appear in the stereotypical Gnome fashion, with thick long beards. They primarily wear red shirts, blue pants and black belts. Each wears a tall pointed hat, normally green or black in color. Many carry backpacks in order to store the underwear.

Gnomes are apparently very sturdy creatures, who can stand-up easily to physical abuse; Cartman striking one with a stick did not appear to harm it, merely prompting it to call him a pussy. Though it should be noted that Cartman is fairly nonathletic and might not be capable of hitting very hard.